Method for monitoring a strip of fabric

Abstract

The tension in a moving web of material is measuring using a measuring roller or cylinder. This tension is repeatedly compared to a threshold value. If the measured value deviates from the threshold value beyond a certain amount, this is used as an indication of web tear or breakage.

What is claimed is:  
     
       1. A method for monitoring a moving web of material including: 
       measuring a first web tension of said moving web of material at a first time;  
       measuring a second web tension of said moving web of material at a second time subsequent to said first time;  
       determining a difference between said first web tension and said second web tension;  
       using said difference between said first web tension and said second web tension as a value of a change of said web tension per unit of time;  
       providing a threshold value of said change of said web tension per unit of time;  
       comparing said value of said change of said web tension per unit of time with said threshold value of said change of said web tension per unit of time;  
       generating a signal when said value of said change of said web tension per unit of time exceeds said threshold value of said change of said web tension per unit of time; and  
       determining the occurrence of a tear in said web of material from said generation of said signal.  
     
     
       2. The method of  claim 1  further including applying said value of said change of said web tension per unit of time to a reference value (BS(n)) of said web tension, and evaluating a function developed from said value of said change of said web tension per unit of time applied to said reference value (BS(n)). 
     
     
       3. The method of  claim 2  further including developing said reference value (BS(n)) from a measured value (BS(n)). 
     
     
       4. The method of  claim 3  further including continuously updating said reference value (BS(n)) of said web tension. 
     
     
       5. The method of  claim 4  further including developing said reference value (BS(n)) of said web tension using an actual value (BS(n+1)) obtained from a previous one of said continually updated reference values (BS(n)). 
     
     
       6. The method of claim 12 further including determining said reference value (BS(n)) from defined production conditions. 
     
     
       7. The method of  claim 1  further including providing a web tension measuring roller, mounting said web tension measuring roller in place, and using said web tension measuring roller for measuring said web tensions. 
     
     
       8. The method of  claim 1  further including providing a web catching device and actuating said web catching device in response to said determining the occurrence of a tear in said web of material. 
     
     
       9. The method of  claim 1  further including providing means for moving cylinders of print units apart in case of a tear in said web of material, and moving said cylinders apart in response to said determining the occurrence of a tear in said web of material. 
     
     
       10. The method of  claim 1  further including providing a print unit and measuring said web tensions downstream, in a direction of web travel, of said print unit.